An electric device has an electrically switchable resistor (2′) comprising a phase change material. The resistance value of the resistor can be changed between at least two values by changing the phase of the phase change material within a part of the resistor called the switching zone (12′) using Joule heating of the resistor. The device comprises a body (24′) encapsulating the resistor, which body comprises at least two abutting regions (26′, 28′) having different thermally insulating properties. These regions form a thermally insulating contrast with which the dimension of the switching zone can be determined without having to alter the dimensions of the resistor. Such a device can be used in electronic memory or reconfigurable logic circuits.